There are strong demands for lower price, more efficient, and quieter motors for driving fans mounted in electric appliances such as ventilating equipment. Since induction motors are not amenable to drastic improvements in efficiency, brushless DC motors using permanent magnets are increasingly being adopted.
In this type of motor, a capacitor provided on a wiring board is covered with a protective case and then molded in using molding resin, as typically disclosed in Unexamined Japanese Patent Publication No. 2001-339909.
This motor is described below with reference to FIGS. 7 and 8. As shown in these Figures, box-shaped protective case 101 made of synthetic resin has door 102 on its front face. A pair of notches 103 continuing from the opening on the front face is provided on a bottom face of protective case 101. A pair of pins 105 of cylindrical aluminum electrolytic capacitor 104 with a closed top face is inserted into these notches 103, and aluminum electrolytic capacitor 104 is housed inside protective case 101. Door 102 is closed to completely enclose a body of aluminum electrolytic capacitor 104 inside protective case 101. Then, as shown in FIG. 7, wiring board 106 is molded in using molding resin 107.
Some of these types of motors also have a reinforcing rib with an electrolytic capacitor disposed sideways inside a component housing case, which has a curved top face with highest part at the center. This is then molded in using molding resin, as typically disclosed in Unexamined Japanese Patent Publication No. 2003-319615.
This motor is described below with reference to FIGS. 9 to 11. As shown in the Figures, protective case 112 is configured with component housing case 113 and cover case 115 coupled to this component housing case 113 using sheet hinge 119. Reinforcing rib 114 is formed on an inner face of component housing case 113 and cover case 115 respectively. Cover case 115 has curved top face 116.
Cylindrical electrolytic capacitor 111 with a closed top face containing electrolytic solution is housed in component housing case 113. A pair of lead terminals 117 of electrolytic capacitor 111 is led out downward through lead-terminal exiting groove 118. Then, cover case 115 is closed, and protective case 112 is molded in together with printed circuit board 121 using molding resin 120.
In these conventional motors, a separate material is used for the protective case to protect the aluminum electrolytic capacitor during molding. This leads to an increased number of processing steps and higher costs. Accordingly, there is demand for a set up to prevent damage to the capacitor without the need for the protective case.
In addition, the top face of the case of the electrolytic capacitor tends to deform in the direction of applied pressure. Therefore, even though the top face is designed to avoid directly receiving the injection pressure of molding resin, the top face may be damaged by the air around the capacitor being compressed. If the top face is damaged, it pushes against a wound element inside the case. This may cause the element and a lead terminal with a different pole to this element to come into contact and thus increase leakage current. Accordingly, there is demand for a reliable way to prevent damage to the top face of case of the capacitor.
In addition, since aluminum electrolytic capacitors contain electrolytic solution, gas is continuously generated by chemical reaction when the current is applied, and the gas escapes from the case through the sealing rubber. This may cause migration. Accordingly, there is demand for a reliable way to eliminate the occurrence of migration.